(a) Technical Field
The present disclosure relates, generally, to a method for controlling a motor. More particularly, it relates to a method for controlling a permanent magnet synchronous motor that is used in electric vehicles such as hybrid vehicles, fuel cell vehicles, and the like.
(b) Background Art
A permanent magnet synchronous motor (PMSM) is a high-power and high-efficiency motor that is widely used in the fields of electric vehicles including hybrid vehicles, fuel cell vehicles, and the like, as well as other industries.
In particular, an interior permanent magnet synchronous motor (IPMSM) is a synchronous motor having a permanent magnet inserted into a rotor iron core. The IPMSM has excellent high-speed durability and drivability, and thus is suitable for use as an electric vehicle motor.
As shown in FIG. 1, according to a conventional method for controlling a permanent magnet synchronous motor, a current command generator 35 receives a torque command Te* and a rotational speed ωrpm of the permanent magnet synchronous motor and generates a d-axis current command id* and a q-axis current command iq* based on current command map data 36a and 36b. 
When the current command generator 35 outputs the generated d-axis and q-axis current commands id* and iq*, a current controller (not shown) generates d-axis and q-axis voltage commands Vd* and Vq* based on the d-axis and q-axis current commands id* and iq*. Thereafter, the permanent magnet synchronous motor is suitably controlled by the generation of three-phase voltage commands Vu*, Vv* and Vw* and by pulse width modulation (PWM) and three-phase current control of an inverter.
Conventionally, however, a predetermined current command is suitably generated and the torque at the corresponding motor speed is suitably generated according to the torque command and the motor rotational speed based on a predetermined reference voltage map regardless of the voltage of a battery as a power source of the motor, i.e., based on a map set at the lowest DC link voltage which meets the output specifications of the motor.
Therefore, the battery voltage variation cannot be reflected in real time, which suitably reduces the voltage utilization of the inverter when the battery voltage increases during operation.
Particularly, in the electric vehicles such as hybrid vehicles, fuel cell vehicles, and the like, since the battery voltage during operation of a vehicle drive motor is suitably higher than the reference voltage at which the map is set, the generation of the current command based on the map set at the reference voltage is disadvantageous in terms of the use of voltage and current.
Accordingly, it is possible to perform linear interpolation using a current command map for each voltage step up to the maximum voltage which is suitably generated while driving a vehicle. However, it requires a large data storage as well as considerable time and effort.
Accordingly, there remains a need in the art for methods for controlling a permanent magnet synchronous motor used in electric vehicles.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.